2. Parthenium integrifolium L. (American feverfew, wild quinine)

Pl. 285 a–d; Map 1211

Plants perennial herbs, with short to more commonly long-creeping rhizomes or a somewhat thickened, tuberous rootstock. Stems 30–100 cm long, usually unbranched below the inflorescence, moderately to densely pubescent with short, stiff, spreading to ascending hairs toward the tip, sometimes also with minute, sessile, spherical, yellow glands, glabrous or sparsely to densely pubescent with stiff, spreading or ascending hairs toward the base. Basal and lower stem leaves long-petiolate, the blades 12–30 cm long, elliptic to ovate, long-tapered to the petiole at the base, angled or tapered to a bluntly or sharply pointed tip, unlobed or those of the largest leaves rarely with a few short lobes toward the base, the margins otherwise coarsely toothed or scalloped, the upper surface sparsely to moderately roughened-pubescent with short, stiff hairs, the undersurface moderately to densely pubescent with short or longer, stiff, spreading hairs, both surfaces also usually with minute, sessile, spherical, yellow glands. Median and upper stem leaves short-petiolate to sessile, the blade mostly 2–15 cm long, lanceolate to ovate, angled or tapered to the petiole or, in sessile leaves, often rounded to shallowly cordate and sometimes somewhat clasping the stem, the margins and surfaces more or less like those of the lower leaves. Involucre 3–6 mm long, 4–10 mm in diameter, the bracts of the outer series slightly shorter than the others, lanceolate to broadly ovate, those of the inner series broadly ovate to nearly circular. Pappus of 2 or 3 slender awns 0.2–0.5 mm long. Fruits 3–5 mm long. 2n=72. May–October.

Scattered nearly throughout the state but uncommon or absent from the northwestern quarter (eastern U.S. west to Minnesota and Texas; Canada). Glades, upland prairies, savannas, openings of mesic to dry forests, and ledges and tops of bluffs; also pastures, railroads, and roadsides.

Wild quinine was a minor medicinal plant for some tribes of Native Americans, who applied poultices of the leaves to treat burns (Moerman, 1998). Although it occurs in other vegetation types, it is a characteristic species of high-quality upland prairie plant communities.

Botanists in Missouri apparently have had trouble distinguishing the two native taxa accepted by Steyermark (1963), P. hispidum and P. integrifolium, as evidenced by the number of specimens with multiple annotations back and forth. Superficially, the two would seem amply distinct, but in fact a number of seemingly intermediate specimens exist for each of the characters used by Steyermark (1963) and Rollins (1950) to separate them. In his monograph of the genus, Rollins noted the broad geographic overlap between the two taxa in Arkansas and Missouri and postulated that hybridization between them probably was occurring, based on his inability to assign some specimens collected in the region to one or the other taxon with certainty. Mears (1975), in a preliminary report to a more detailed monograph of the complex that regrettably was never published, chose to treat the two members of the P. integrifolium complex as varieties (he recognized five total varieties in P. integrifolium). Mears noted that var. integrifolium occurs virtually throughout the species range, with his other four varieties circumscribing more geographically localized variants, sometimes adapted to somewhat different habitats than those of the typical variety. Clearly, the situation requires more detailed biosystematic study. Whether the Missouri plants represent two species whose boundaries are slightly blurred by occasional hybridization or a widespread species with an incompletely distinct variety adapted to somewhat drier sites cannot be determined without more intensive study in the field, herbarium, and laboratory. For the present, the two are accepted provisionally as varieties, in recognition of the difficulties involved in the determination of some specimens.